Interesting. On the one hand, they do argue that to save the human race we need to solve climate change. And then the other, to solve climate change we need to control this invasive species.
In the UK recently we had a televised lecture which dealt with global population statistics. It was fascinating, and actually proved that after a massive explosion in the last century, population growth was actually decelerating now, and generally families were getting smaller. Big families are not a product of tradition or religion but of necessity. If 4 of your kids are likely to die before reaching an age where they can contribute to household productivity, you're going to have 6. If you can find it, check out " Don't Panic - The Truth About Population ".
It also showed that there IS enough food to feed the current and future populations, but that it is wrongly distributed.
As regards productivity, Big Oil, vested interests and the greed of those at the top at the expense of those at the bottom of the pile. If our cost of living wasn't so disastrously high, we'd be able to afford to make stuff ourselves instead of relying on cheap imported goods. If our governments thought more about the benefits of self-sufficiency and less about winning on the International money market maybe we'd start enforcing our tax laws more rigorously, and then maybe we wouldn't need to worry so much about GDP?
Just my random, meandering pointless 2p.